Several years ago, a self-described native Spanish speaker posted the following question on a WordReference.com language forum under the subject head "laughing one's butt off":
I think I know the meaning of this expression, but i'm not sure so could you please help me confirm it?
A minute later, "Greenie" provided a concise, though admirably comprehensive, explanation:
The idea is that you laugh so hard that your butt falls off. Of course this doesn't actually happen.
No, not actually. But it turns out that we've been figuratively verbing various parts of our bodies off since at least the 1840s, when Charles Dickens, at the very end of a letter to his close friend Thomas Mitton, apologized for his sloppiness: "I have made a great many erasures and mistakes in this short space, but I have nearly written my head off this morning and am dismally stupid."
Dickens was understandably foggy from too many hours inside The Old Curiosity Shop, which he was likely writing at the time, but people were soon self-decapitating in alarming numbers and imaginative ways—smoking, screaming, even yawning their own heads clear off. In his 1871 (Burlesque) Autobiography and First Romance, Mark Twain purports that a 15th-century ancestor of his, Beau Twain, had "a beautiful, beautiful hand. And he could imitate anybody's hand so closely that it was enough to make a person laugh his head off to see it."
It wasn't until the less decorous, post–World War II era in American literature, however, that our asses started falling off, in print anyway, from continuous labor, extreme temperatures, and any number of other assiduities and hardships. In the 1940s, in Norman Mailer's The Naked and the Dead, we get the following inner dialogue from a character named Roy, who was stood up by a woman:
The goddam bitch, none of them can fool me, they all put out for the right guy, but they just don’ gimme a chance, the caards are stacked against me, it’s the goddam breaks I just never get them. I work my ass off at the club, and what does it get me?
In the 1950s, The Catcher in the Rye's Holden Caulfield—"If there's one thing I hate it's the movies. Don't even mention them to me," he says in the first paragraph of the novel—describes a particularly "putrid" war film:
It ends up with everybody at this long dinner table laughing their asses off because the great Dane comes in with a bunch of puppies. Everybody thought it was a male, I suppose, or some goddam thing. All I can say is, don't see it if you don't want to puke all over yourself.
If Holden were haunting the campus of Pencey Prep today and fancied hyperbolically verbing off a body part, he'd no longer be limited to just his head or his tail. Nowadays, we routinely lose our tits to industry and our faces to starvation, though our asses remain more likely to go, and nowhere more so than in the initialism-mad online speak where LMAO, as shorthand for "laughing my ass off," was born.
In 1990, in an online game of Advanced Dungeons & Dragons, Torquin (an elven male Ranger) typed "LMAO!" after Sayaka (a human female Monk) suggested that Daldin (a dwarf male Fighter) might want some hijiki for lunch. (I guess you had to be there.) In any case, we've been L-ing our A’s O ever since, though Internet culture, with its constitutional allergy to understatement, soon upped the intensity with LMFAO, or "laughing my fucking ass off," and LMA with multiple O’s.
In an online forum in New Zealand in the late 1990s, "Sarndra" used both LMAOO and LMAOOO, and, when asked by others what the abbreviations meant, explained:
Laff my arse off and off...depending on how many o's there are ;-) according to how humourous i find things
Either the world has become more uproariously funny in the past quarter century or we're all too easily amused, since it's not uncommon now to find an LMA on Twitter with 10 or 20 O’s, leaving one to wonder whether someone simply nodded off on his keyboard.
This whole bizarre business of verbing off our own body parts likely grew out of the earlier linguistic possibility of verbing off someone else's, as in the expression beating someone's head off, meaning to best them decisively. And with all this amputational punishment inflicted at the tongues of ourselves and others, it's a wonder any of us get through life intact. We should be limping along blindly, headless, and without our asses, praying that we don't freeze our dicks off. Of course, as Greenie so helpfully pointed out, this doesn’t actually happen.